Apparatus for dispensing a vapour into an air flow

ABSTRACT

An apparatus for dispensing a vapour of a liquid into a ventilation system includes a vessel for holding the liquid, a heater for heating the liquid in the vessel to form a vapour, and means for delivering the vapour into the air flow passing through a passageway of the ventilation system. The liquid may be an essential oil or other liquid. An aerator may be used to deliver the vapour into the air flow. The apparatus may also include one or more additional liquid reservoirs, a controller which regulates the operation of the heater in response to user control, an air flow detector, and data stored in a controller memory.

TECHNICAL FIELD

[0001] The present invention relates to air conditioning and otherventilation systems and more particularly to an apparatus and method ofintroducing essential oil vapours into an air flow of a ventilationsystem for health and deodorising purposes.

BACKGROUND OF THE INVENTION

[0002] Building air conditioning, central heating and other ventilationsystems are known to recirculate odours and microorganisms such asbacteria and fungi which may breed in the air passages of theventilation system. It is believed that such microorganisms may bedetrimental to the health and comfort of occupants of the building.

[0003] WO 88/00199 discloses a method of treating air conditioningsystem air by introducing a spray of oil of Melaleuca of a particularmean droplet size, and a spray composition comprising the oil dissolvedin liquid carbon dioxide. However, there remains a need for a method andapparatus which relatively inexpensive, convenient and scaleable to suitlarge or small scale air conditioning or ventilation installations.

OBJECT OF THE INVENTION

[0004] It is an object of the invention to provide an apparatus andmethod of introducing essential and/or fragrant oil vapours into the airflow of a ventilation system, so as to deodorise and/or disinfect theventilation air, which meets some or all of these needs.

SUMMARY OF THE INVENTION

[0005] A first form of the present invention provides an apparatus fordispensing a vapour into an air flow of a ventilation system, saidapparatus including

[0006] a vessel for holding a liquid;

[0007] a heater for heating the liquid in the vessel to causeevaporation of liquid in the vessel; and

[0008] means for delivering vapour from said vessel into said air flowof the ventilation system.

[0009] Preferably, the apparatus further includes means for aeratingsaid liquid to create gas bubbles therein. Preferably, said aerationmeans includes a gas tube located within said vessel, said tube having aplurality of gas holes therein and gas supply means in communicationwith said tube adapted to pump a gas through said holes to create saidbubbles. Preferably, said gas is air.

[0010] In one preferred form, the apparatus further includes a usercontrol interface remote from said vessel for user control of saidapparatus, including switch means for said apparatus. Preferably, saiduser interface further includes input means for adjusting an amount ofsaid vapour delivered to said air flow. Preferably, control means of theapparatus includes a temperature regulator which regulates said heatingmeans responsive to the vapour adjustment input means by adjusting atemperature setpoint of the temperature regulator.

[0011] Preferably, the control means includes means for detecting aquantum of said air flow and adjusting evaporation of said liquid tomaintain a desired concentration of said vapour in said air flow.

[0012] In a further preferred form, the apparatus includes a reservoirin communication with said first vessel for holding a supply of saidliquid, and means for transferring said liquid from said reservoirvessel to said first vessel to maintain a predetermined level of saidliquid in said first vessel.

[0013] Preferably, the apparatus includes a plurality of said vesselsfor holding different liquids and a user interface including userselection means for selective activation of heating means in saidvessels. Preferably, said user selection means further selectivelyactivates one or more valves closing off vapour delivery from those ofsaid vessels containing liquids not selected by the user.

[0014] Preferably, said liquid is an essential oil or perfume.Preferably, said essential oil is Tea-tree (Melaleuca), Eucalyptus, pineor lemongrass oil, or blends therof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further preferred embodiments of the invention will now bedescribed with reference to the accompanying drawings, in which:

[0016]FIG. 1 is a schematic elevation of an oil vessel and deliveryconduit apparatus according to a first embodiment of the invention;

[0017]FIG. 2 is a schematic illustrating an installation of the vesseland associated control apparatus; and

[0018]FIG. 3 is a schematic elevation of a multi-compartment oil vesselaccording to a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019]FIG. 1 is a schematic depiction of an apparatus 5 for dispensing avapour 10 into an air flow 15 flowing through an air passage 17 such asa supply or return air duct or plenum of a building ventilation system.

[0020] The apparatus is adapted for installation with a variety ofcentral heating and ventilation system types, and air conditioningsystems such as ducted air conditioning, split systems and rooftoppackages. The apparatus may be installed with the original systeminstallation, or retrofitted to an existing installation.

[0021] The apparatus of FIG. 1 includes a first vessel 20 for holding apredetermined quantity of an essential or fragrant oil 25, heating means30 for heating the liquid in the vessel 20 to cause evaporation of theliquid from the vessel. The apparatus further includes a vapour deliveryconduit 32 communicating between the head space above the liquid in thevessel and air passage 17. The apparatus will typically be installed inthe roofspace of the building, adjacent to the evaporator of the airconditioning system, although in the case of a split system airconditioning unit may be incorporated in or attached to the evaporator(in cooling mode).

[0022] The apparatus further includes an aerator 35 for pumping bubblesof gas, typically air, through the oil 25 in the vessel 20. The aeratorincludes a tube 45 with perforations 55 therein, located at the base ofthe vessel 20. Aerator means 35 includes pump 62 adapted to pump airthrough an air hose into the tube 45. The air then passes through theperforations 55 to bubble the air through the oil in the vessel, toincrease transfer of the oil vapour into the air flow 15. Preferably,there is provided a valve or other flow restriction means to adjust theaeration rate, for example from about 1 to 5 litres per minute, to helptransport sufficient vapour to sustain a vapour concentration of from 1to 10 PPM in a typical ducted air conditioning system.

[0023] The vessel 20 will preferably hold a predetermined volume, forexample 1.0 litres, of an antimicrobial and aromatic essential oil oroil blend such as tea-tree (genus melaleuca) for deodorising, or pine,lemongrass and/or eucalyptus oils for helping relieve the symptoms ofsinus congestion, colds or influenza, or essential oils or blends havingaromatherapeutic properties such as a ‘revitalising’ oil or a ‘calming’oil such as lavender.

[0024] The vessel preferably is constructed of corrosion resistant metalsuch as brass or stainless steel, or other material with good heattransfer properties, to facilitate transfer of heat from the heatingelement 30 into the oil in the vessel. The outside of the vessel ispreferably insulated with a thick layer of polyester glass or similarinsulative material to limit heat loss from the vessel in winter andheat gain in summer.

[0025] The vessel is fitted with an air-tight lid, with a connection tothe vapour delivery conduit 32. The conduit slopes upward from thevessel to the duct, so that any vapour which condenses on the inside ofthe conduit wall will drain back into the vessel. A small wattageheating element 65 may also surround the delivery conduit to limitcondensation in winter.

[0026] The lid, or the conduit, may further include a solenoid cut-offvalve 70 for closing off delivery of vapour to the duct when the systemis turned off, thus preventing unwanted evaporation of the oil.Furthermore, where the vapour is to be introduced into the higherpressure, supply side of the ventilation system, the conduit may alsoinclude a one-way check valve to prevent backflow.

[0027] The heater 30 includes one or more heater elements incorporatedin the base of the vessel 20, so that the heat generated will risethrough the oil in the vessel. The maximum wattage of the heaterelements required will depend on the maximum oil vaporisation capacity,which in turn depends on the maximum air flow of the ventilation systemto which the apparatus is installed, and the required oil vapourconcentration. For a typical residential ducted air conditioning system,a heater power of 100-300 W can sustain an oil evaporation rate ofapproximately 5-25 g/hour, which is sufficient to produce a vapourconcentration in the ventilation air flow of from 1-10 PPM.

[0028] The heater further includes a temperature sensor 75 inside or inheat transfer communication with the vessel, which regulates operationof the heater elements by switching off power to the heating elementswhen the desired oil temperature in the vessel is reached.

[0029]FIG. 2 schematically illustrates an installation of the system,including the control system for regulating the resultant concentrationof oil in the recirculated air.

[0030] The illustrated apparatus includes an oil vessel 20 and deliveryconduit arrangement, communicating with an air duct in the roofspace 80of a building, generally as described above with reference to FIG. 1.

[0031] The system of FIG. 2 further includes an oil reservoir 85,typically of larger capacity than the first vessel, for example of 5-20L, and an oil transfer pump 90 controlled by an oil level switch in thevessel, such as float switch 95. Upon the oil level in the vessel 20falling below a predetermined level, the float switch causes operationof the oil transfer pump 90 to pump from reservoir 85 to the firstvessel 20 until the level in the vessel again reaches the requiredlevel. In this way, a relatively constant oil level may be maintained inthe first vessel, maintaining a constant length of the pathway of thebubbles through the oil so that the oil evaporation rate at the settemperature is predictable.

[0032] The reservoir 85 may be situated at a location accessible forrefilling with oil, and may include an inlet hose 92 leading to a fillerplate 93 with a filling port 95 mounted on a wall of the building or atsome other convenient location.

[0033] Operation of the system is regulated by a central controlprocessor 100 connected to a the electricity supply. The functions ofthe controller will be described in more detail below.

[0034] The controller has inputs for receiving data from a memory device105, the temperature sensor 75, float switch 95, an air flow sensor 110which detects air velocity in the duct 17, a system maintenance controlinterface 115 and a user control interface 120.

[0035] The controller has outputs for controlling operation of the airpump 62, heating elements 30 and 65, solenoid valve 70, and oil pump 90.

[0036] The air flow sensor 110 is preferably a hot-wire anenometer orsimilar which measures the duct air velocity in m/s, from which thevolume of air flow may be calculated.

[0037] The maintenance interface 115 is adapted for initial set-up andsubsequent adjustment of the system by a technician and has a wide rangeof functionality. Typically, the maintenance interface will be situatedeither in the roofspace 80 with the controller 100 or portable so thatthe technician can carry a single maintenance interface device such as apersonal display device to service a number of installations.

[0038] The user interface will typically be remote from the controllerand vessel, and be mounted on an internal wall 125 of the buildingspace, readily accessible by the occupants of the air conditioned space.The user interface has a limited fuctionality. For example, in theillustrated embodiment the user interface has an on-off switch and avapour concentration adjustment control 130. The user interface mayfurther include an oil selection switch for selecting between oils, aswill be described later with reference to FIG. 3, and a timer forpre-programming operation of the system for example to run the systemfor an hour before the occupants are due to arrive home of an evening.

[0039] In use, the memory device 105 of the controller 100 is programmedwith empirical evaporation rate against vessel temperature data for thetype of essential oil or oils to be placed in vessel 20. Typically, overthe temperature range over which the apparatus is to used, therelationship will be sufficiently linear to be approximated by a line ofbest fit according to the formula:

R=MT+B,

[0040] where R is the evaporation rate in grams/hour,

[0041] T is the vessel temperature in ° C., and

[0042] M and B are coefficients.

[0043] The relationship between the evaporation rate and temperature fora particular type of oil may thus be derived by the controller fromvalues of M and B stored in the controller memory.

[0044] Also entered in the controller memory by the technician is theair duct diameter, from which the cross-sectional area of the air duct,so that the air flow volume may be derived by multiplying the air flowvelocity by the calculated cross-sectional area of the duct

[0045] Using the maintenance interface, the technician sets a baselinevapour concentration setpoint for the system, in parts per million. Theuser interface 120 includes a control knob 130 which allows usercontrolled variation of the vapour concentration up to a certain maximumpercentage, for example 100%, above or below the setpoint.

[0046] When the system is switched on at the user interface, thecontroller uses the baseline vapour concentration, as modified by theuser control knob setting, and the air flow volume calculated from theair flow sensor reading to calculate the required oil evaporation ratefrom the vessel. The controller then uses the stored correlation betweenevaporation rate and temperature to derive a vessel temperaturesetpoint, and controls the vessel heating element according to feedbackreceived from the temperature sensor to maintain the requiredtemperature. Typically, the vessel will be operated at a temperaturerange of about 40-70° C., for example 50-60° C., to maintain a vapourconcentration of about 1-5 PPM, at which concentration the vapour willproduce a subtle but pleasant fragrance. The air pump 62 is activatedand solenoid valve 70 opened to allow the vapour to be transported intothe air duct and thus distributed through the building space.

[0047] If the vessel temperature is above the setpoint, as may be thecase in summer where roofspace temperatures can reach 70° C., thecontroller will turn off the air pump to reduce the transport of vapourinto the air duct.

[0048] When the oil level in the vessel drops sufficiently to actuatethe level switch 95, the controller activates the reservoir oil pump 90to top up the oil level in the vessel 20.

Example

[0049] An example illustrating the control parameters of the controllerand the maintenance and user interfaces of FIG. 2 are further describedbelow.

[0050] The maintenance interface allows the continuous interrogation ofthe controller state and the configuration of the controller to theparticular requirements of the site at which it is installed. Themaintenance interface is accessed through a portable display devicehaving on/off, menu advance/select, up and down control keys, and an‘alert’ light. The display device may be connected/disconnected from thescent controller at any time.

[0051] Within the controller, each operational parameters is assigned aunique address. The current value of a single parameter may be viewed byselecting its address upon the display device. Parameters which formpart of the controller's configuration may be changed by the technician.The new value will take effect when the address is advanced/altered todisplay a different parameter.

[0052] Parameters which display current state information, measuredvalues or values derived from measurements, are not able to be changedby the user. These values are continually updated as conditions withinthe controller change.

[0053] Alteration of the parameter address is effected by selecting themenu advance key while operating the up and down keys. Alteration of theconfiguration parameter values is effected by operating the up and downkeys while the desired address is being displayed. If these keys areselected for an extended period, a “repeat” function is activated,causing the value to rapidly increase/decrease. Increases/decreases tothe parameter value will not be possible if the value has reached itsrespective maximum/minimum value.

[0054] The maintenance controller has the following “error states”. Whenan error is detected, the unit discontinues operation and flashes the“Alert” light on the interface control panel. Operation can be restoredby the user selecting the “Off/On” button. When an error is encountered,if the maintenance interface is not currently modifying a value, theaddress is forced to the “error” address. The error states are asfollows:

[0055] 0. No Fault

[0056] The system is operating normally.

[0057] 1. Fluid Level

[0058] The correct fluid level could not be achieved within thenominated period. This is not considered to be a “serious” fault and isdistinguished by illuminating the “Alert” light, but not flashing it.

[0059] 2. Lost Configuration

[0060] The system internally stores all configuration parameters withina semi-permanent storage area. In the case of a serious malfunction,this memory can become corrupt. In the absence of valid configurationinformation, the controller is unable to function. This fault can onlybe cleared by operating the maintenance interface up and down keys (thusdemonstrating that the parameters have been reviewed and reset).

[0061] 3. Airflow Sensor

[0062] The airflow sensor has been unable to make a correct airflowmeasurement. This is probably due to a wiring/sensor fault, or possiblydue to dirt accumulation on the sensor.

[0063] 4. Heater

[0064] The system is unable to correctly control the fluid chambertemperature. This is probably due to a fault in the heater ortemperature sensor. It may possibly be die to an excessive ambienttemperature.

[0065] Display parameters which are available for display only, andtheir addresses are as follows:

[0066] 0. Chamber Temperature

[0067] The current temperature of the fluid chamber, expresses in °C.÷10, i.e. the display shows XX.X ° C.

[0068] 1. Chamber Setpoint

[0069] The fluid chamber temperature which the controller is trying toachieve, expressed in ° C.÷10, i.e the display shows XX.X ° C. If theheater is not currently active, the value 0 is shown.

[0070] 2. Fault Indication

[0071] The system error state value (see the discussion of the errorsabove), or 0 if there is no error.

[0072] 3. Airflow

[0073] The current airflow reading, expressed in m/s÷10, i.e. thedisplay shows XX.X m/s. If the airflow sensor is currently inactive orhas not been active for a sufficient time to produce a stable reading(typically about 1 minute), the value 0 is displayed.

[0074] The airflow sensor is activated when the system is “On” i.e. theuser interface “Active” light is steady red or green. The airflow sensoralso activated when the system is in “Service” mode (see below).

[0075] 4. Knob Reading

[0076] The setting of the user control panel knob, expressed as a valuefrom 0 to 100.

[0077] 5. Air Volume

[0078] The current air volume reading (the amount of air passing theairflow sensor each second), expressed in 1/sx10, i.e. the display showsXXX01/s (where XXX are the display digits). If the airflow sensor iscurrently inactive or has not been active for a sufficient time toproduce a stable reading (typically about 1 minute), the value 0 isdisplayed.

[0079] This value is derived by combining the air velocity measurementwith the configured duct diameter.

[0080] 6. Derived Scent Concentration

[0081] The scent concentration which the controller will attempt tomaintain within the airstream, expressed in PPM÷100 i.e. the displayshows X.XX PPM.

[0082] This value is derived by combining the “Baseline ScentConcentration” with the setting of the user control panel knob. The knobsetting allows a ±30% variation to the “Baseline Scent Concentration”.

[0083] 7. Evolution Rate

[0084] The rate at which the controller is attempting to evaporate fluidfrom the chamber, expressed in g/h÷10, i.e. The display shows XX.X g/h.

[0085] This value is derived from the “Derived Scent Concentration” andthe mass of the air passing through the system (which is derived fromthe air volume and the known density of air).

[0086] The parameters which configure the operation of the system andare available for modification, are as follows:

[0087] 8. Service Setpoint

[0088] If this value is set to a non-zero value, the system enters a“service mode”, in which the “Chamber Setpoint” is fixed at the valuedefined by the service setpoint. This value is expressed in ° C.÷10,i.e. the display shows XX.X ° C. This value can range from 0 to 99.9° C.

[0089] While service mode is active, the fluid pump will not operate andthe user control panel flashes both lights.

[0090] 9. Duct Diameter

[0091] This value defines the diameter of the duct at the point wherethe airflow measurement is being taken, expressed in cm, i.e. thedisplay shows XXX cm. This value can range from 0 to 225 cm.

[0092] The duct is assumed to be round. If a different cross section isbeing used, it must be converted to an equivalent circular crosssection.

[0093] 10. Baseline Scent Concentration

[0094] The scent concentration which is configured for this site,expressed in PPM÷100, i.e. the display shows X.XX PPM. This value canrange from 0 to 99 PPM, though in practice will typically range fromabout 1-10 PPM.

[0095] This value is modified by the setting of the “user control panelknob” to yield the actual scent output (see “Derived ScentConcentration” above).

[0096] 11. Fluid M Coefficient

[0097] 12. Fluid B Coefficient

[0098] These parameters define the evaporation characteristics of thescent fluid which is being used, as previously described. These valuescan range from 0 to 225 and 0 to 999 respectively.

[0099] These values are specific to the fluid being used and aredetermined by previous testing of the fluids.

[0100] 13. Chamber Fill Timeout

[0101] The amount of time which the controller will allow the fluid pumpto run, after which a “fluid level” error is declared. This value isexpressed in minutes÷10, i.e. the display shows XX.X minutes. This valuecan range from 0 to 50.0 minutes.

[0102] 14. Chamber Run Temperature Range

[0103] This defines how close the oil vessel temperature must be to the“Chamber Setpoint” before it is considered to the “at temperature”. Thevessel temperature must fall within this range before the air pump willoperate.

[0104] This value is expressed in ° C.÷10, i.e. the display shows XX.X °C. This value can range from 0 to 25.5° C.

[0105] 15. Airflow Calibration M

[0106] 16. Airflow Calibration B

[0107] These parameters define the characteristics of the airflow sensorand are specific to the sensor which is attached to the system. Thesevalues can range from 0 to 255 and 0 to 999 respectively.

[0108] Each sensor is labelled with these values during productiontesting.

[0109] 17. Chamber Temperature Calibration

[0110] This parameter defines the characteristics of the controller andtemperature sensor in combination. This value can range from 0 to 100.

[0111] Each system (consisting of a controller and temperature sensor islabelled with this value during production testing.

[0112]FIG. 3 illustrates an alternative vessel arrangement adapted toallow for user multiple oils to be used in the system.

[0113] The vessel 320 of FIG. 3 is formed as two or more separate oilchambers 318 separated by an air gap 319 or insulation material (notshown) to prevent substantial heat transfer between the chambers. Eachchamber has its own heating elements 330, air tube 345, temperaturesensor 375 and level switch 395, controlled by the controller. Eachchamber will also have its own reservoir vessel and oil pump(not shown).Separate air pumps, or a single air pump with means for switchingbetween chambers, may be used.

[0114] Each chamber may have a separate lid or, as illustrated, thevessel lid may comprise a vapour manifold with passages 332communicating with respective of the chambers, each with its ownsolenoid valve 370.

[0115] It is envisaged that the chambers will be filled with oils ofdifferent scents and characteristics, for example a ‘invigorating’ oilin one chamber and a ‘relaxing’ oil in the other. The user interfacewill have a switch allowing the user to select which of the oils is tobe distributed, so for example the user may select the invigorating oilin the early evening when arriving home from work, and select therelaxing oil later in the evening.

[0116] The controller will be programmed with the M and B values for theoils in each of the chambers, and will selectively operate the chambercorresponding to the oil selected at the user interface, in the mannerpreviously described. The solenoid valves for the other chambers willremain closed.

[0117] It is envisaged that a typical installation will be set to atrace vapour concentration, for example 1-5 PPM, at which the scent isjust detectable, and in typical residential installations might be runfor only a few hours per day. However, in commercial establishments itmay be desirable to run the system full time at somewhat higherconcentrations to counteract odours such as cigarette smoke.

[0118] While particular embodiments of this invention have beendescribed, it will be evident to those skilled in the art that thepresent invention may be embodied in other specific forms withoutdeparting from the essential characteristics thereof. The presentembodiments and examples are therefore to be considered in all respectsas illustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than the foregoing description,and all changes which come within the meaning and range of equivalencyof the claims are therefore intended to be embraced therein. It willfurther be understood that any reference herein to known prior art doesnot, unless the contrary indication appears, constitute an admissionthat such prior art is commonly known by those skilled in the art towhich the invention relates.

1. Apparatus for dispensing a vapour into an air flow of a ventilationsystem, said apparatus including a vessel for holding a liquid; a heaterfor heating the liquid in the vessel to cause evaporation of liquid inthe vessel; and means for delivering vapour from said vessel into saidair flow of the ventilation system.
 2. Vapour dispensing apparatusaccording to claim 1, further including means for aerating said liquidto create gas bubbles therein.
 3. Vapour dispensing apparatus accordingto claim 2, wherein said aeration means includes a gas tube locatedwithin said vessel, said tube having a plurality of gas holes thereinand gas supply means in communication with said tube adapted to pump agas through said holes to create said bubbles.
 4. Vapour dispensingapparatus according to claim 3, wherein said gas is air.
 5. Vapourdispensing apparatus according to claim 4, including means for adjustingthe rate at which said gas supply means pumps the air.
 6. Vapourdispensing apparatus according to claim 1, further including a usercontrol interface remote from said vessel for user control of saidapparatus, including switch means for said apparatus.
 7. Vapourdispensing apparatus according to claim 6, said user control interfacefurther including input means for adjusting an amount of said vapourdelivered to said air flow.
 8. Vapour dispensing apparatus according toclaim 7, including control means including a temperature regulator whichregulates said heating means responsive to said vapour adjustment inputmeans
 9. Vapour dispensing apparatus according to claim 8, wherein saidcontrol means adjusts a temperature setpoint of said temperatureregulator.
 10. Vapour dispensing apparatus according to claim 1,including control means including means for detecting a quantum of saidair flow and adjusting evaporation of said liquid to maintain a desiredconcentration of said vapour in said air flow.
 11. Vapour dispensingapparatus according to claim 1, further including a reservoir incommunication with said vessel for holding a supply of said liquid, alevel detector for detecting a liquid level in said vessel and means fortransferring said liquid from said reservoir to said first vessel tomaintain a predetermined level of said liquid in said vessel.
 12. Vapourdispensing apparatus according to claim 1, including a plurality of saidvessels for holding different liquids and a user control interfaceincluding user selection means for causing selective activation ofheating means in said vessels.
 13. Vapour dispensing apparatus accordingto claim 12, wherein said user selection means further selectivelycauses activation of one or more valves closing off vapour delivery fromthose of said vessels containing liquids not selected by the user. 14.Vapour dispensing apparatus according to claim 1, wherein said liquid isan essential oil or perfume.
 15. Vapour dispensing apparatus accordingto claim 14, wherein said liquid is an essential oil selected fromtea-tree (Melaleuca), Eucalyptus, pine or lemongrass oil, or blendsthereof
 16. Vapour dispensing apparatus according to claim 1, whereinsaid air flow is in an air passage of an air conditioning system.
 17. Amethod of dispensing a vapour into an air flow of a ventilation system,including the steps of: providing a vessel holding a liquid to bevaporised; heating the liquid in the vessel to cause evaporation ofliquid in the vessel; and delivering vapour from said vessel into saidair flow of the ventilation system.
 18. A method according to claim 17,further including aerating said liquid in the vessel to create bubblestherein.
 19. A method according to claim 18, further including adjustingthe temperature of the liquid in said vessel to control a concentrationof vapour in said air flow.